I want to show my members that their posts and content truly belong to them, considering my forum's TOS grants me a license to 'display' and have their content on my server.
I know Discourse has this option; don't know if NodeBB would be willing to do the same. It's one of those major 'selling points' that I can't part with due to my forum's nature. It would be like google's takeout, where a user clicks a button to prep a 'takeout' download and they are then notified when the download is ready.
A separate, possible option would be to allow a user to download a specific topic and its posts if they participated in that topic, and the topic was closed. The opening poster could have a separate checkbox within a specific category that is checked would make the topic downloadable, but only if the topic is closed. That way a 'takeout' can be created upon closure for allowed users to download.
Finally, the third possible option allows the concept of PMs blend with chat, by allowing a member to save a chat history in a similar fashion. It could also de-clutter said history by deleting the history from the server once it is downloaded.
This is similar to 'print this' options from older forum software, but I'd rather have it as a download so the user can take the data and present it as they see fit.
The main application for this is writing and play-by-post freeform roleplay. When I used to RP on software like phpBB and the like, I'd download and save the 'print' page to achieve this. Now I use chat and instant messengers, which auto-logs for me, hence allowing me to keep my work.
I can see this apply to any other situation, especially if a member is allowed to delete their own account. That way they can take their writing, images and content with them. It would be only fair to allow it so they feel less apprehensive signing up in the first place. As before, I speak from experience. If I can't download my content, I won't upload my content.